goin postal!!!

somebody help please!!! i can not get some of my rads to work usually the one closest to the boiler and the one furthest away i have attempted to bleed but only got a little air out (do you do this with pump running?).the house is 4 years old with a potterton suprima 30 boiler 4 rads up and 4 rads down controller - ep2002 room stat prt2 and water stat ptt2 both never reach set temp (30&55) but the boiler always locksout on temp reached! the pump is set at full speed captain and ive hit it with a mallet, it also runs all the time unless you select heating only and then it wont run at all.
attempted to balance the system (using advice from you guys out there,thanx) but the boiler never stayed in long enough and by the time it came back on none of the bloody thing would get hot!!!!! have tested all my trv\\\'s ok and have checked loft tanks and both are full exept small one has a fair bit of brown gunk in the bottom is this usual? anyway im lost can anybody shed any light on my cold house? my missus would be very greatfull! to me ha thanx.

Try diverter valve.

Don't know about he rads not getting hot but, the problem with the pump running all the time & the boiler locking up is usually down to the pcb on the suprima.

thanks oilman and keego for your replys, do you mean change the diverter for a new one? and does that include changing the eleky motor ontop? will try that first before taking the boiler apart thanx.